Cw HF Chemical Laser Research Articles

Line suppression and single line performance of a cw HF chemical laser

A contactless interference surface testing method is described that is capable of creating fringe patterns with fringe separations corresponding to a surface deformation of a quarter-wavelength of the illumination light. Contrary to common Fizeau fringes where the interference pattern occurs by superposing two wavefronts, the described method is based upon a superposition of four wavefronts. These wavefronts are created by a diffraction transmission grating which is contactlessly placed over the surface to be tested. Basically, this technique provides a beat frequency pattern with adaptable fringe separation. Practical applications of this method to semiconductor silicon wafers are presented.

Frequency stability of a cw HF chemical laser

A new scheme for measuring the frequency stability of a cw HF chemical laser is described. It is based on the measurement of the beat-frequency spectrum of longitudinal modes and the mode-pulling effect in a high-gain medium. The mode-pulling effect can also be used to actively stabilize the laser frequency. Experimental measurements on the mode pulling and the stability of a free-running cw HF chemical laser agree with theory and other experimental measurements.

Temperature measurement in a CW HF chemical laser plenum

Abstract : The temperature of a SF6-He gas mixture in the plenum of a supersonic diffusion laser was measured by observing spectra of the HF(v) molecules when trace amounts of H2 were injected into the hot plenum gas. Because the plenum pressures were relatively high and the mean free path very short, rotational equilibrium was expected to be obtained. Thus, the rotational temperature obtained from the observed spectra was expected to equal the gas translational temperature. Precision of the temperature was + or - 10% largely because of the limited precision involved in the measurement of the slope of the intensity data. The observed values are about 10 to 36% higher than temperatures obtained from a pressure ratio method. This difference is probably because of the wall heat loss that occurs between plenum and throat, which was not taken into account in the pressure ratio method.

Spectroscopic and infrared measurements on the mesa CW HF (DF) chemical laser

Spectroscopic and infrared measurements on the mesa CW HF (DF) chemical laser

Some experimental results with stable selected-line resonators in a relatively high gain cw HF chemical laser

Some experimental results with stable selected-line resonators in a relatively high gain cw HF chemical laser

Comparison of H2 and HBr as cavity fuels in a cw HF laser

H2 and HBr are compared as cavity fuels in a 1-kW arc-driven cw HF chemical laser. Closed-cavity power is presented as a function of fuel flowrate and lasing-axis position. Peak power observed was ∼350 W with HBr, ∼600 W with HBr and He, and ∼1100 W with H2. Spectral content of the laser beam indicated dominant 1–0 and 2–1 vibrational transitions with H2, and 2–1 and 3–2 transitions with HBr.

Linewidth parameters from the Lamb dip in a cw HF chemical laser

The Lamb dip in the power spectrum of a cw HF chemical laser has been observed. The width and depth of this dip were measured as a function of the partial diluent pressure (He or N2) of the lasing mixture. From these measurements the Lorentzian linewidth parameters γHF–He and γHF–N2 for the pressure-broadened laser transitions were found to be about 4 and 18 MHz/torr, respectively.

Performance of cw HF Chemical Laser with N2 or He Diluent

Recent experimental results on the performance of a continuous HF (or DF) chemical laser are reported. In this device, an arc-heated diluent is mixed in a plenum with SF6 to provide F atoms. The mixture is expanded to form a supersonic jet into which H2 (or D2) is diffused. Population inversion and lasing are due to the reaction H2+F=HF(v)+H; v≤3 and Δ H=−31.7 kcal. Power levels above 1 kW have been obtained in a N2 diluent gas flow, and levels above 1.7 kW have been obtained in a He diluent gas flow. Specific power yields are 43 and 108 kW sec/lb for the N2 and He systems, respectively. The variation of laser power and efficiency with cavity optical axis location and SF6 mass flow are reported for both N2 and He systems. A spectrum of the HF laser operating in a He flow is also presented that gives evidence of v=3 partial inversion.